Shuttle shifting for a continuously variable transmission

Abstract

A shuttle shifting method for a continuously variable transmission automatically selects a manner of shuttle shifting as a function of certain monitored conditions. As one alternative, the direction of operation of the transmission is changed prior to reducing the vehicle speed to zero, and tilt of a swash plate of the hydrostatic power unit of the transmission is held substantially constant, for achieving fast, smooth shifts at faster starting and ending vehicle speeds, without coming to a complete stop. In another alternative, for slower starting and ending speeds, or other conditions such as a temperature condition is present, the vehicle is stopped by changing swash plate angle before effecting a directional change of the transmission and the swash plate.

What is claimed is: 
     
       1. A method of automatically operating a continuously variable hydro-mechanical transmission of a vehicle responsive to a commanded shuttle shift, comprising steps of:
 determining a start speed of operation of the transmission and a commanded end speed thereof for the shuttle shift; and 
 a. if the start speed and the end speed are greater than predetermined first threshold values therefor, then performing the shuttle shift by changing a direction of operation of the transmission while holding a swash plate of a hydrostatic power unit of the transmission tilted in one direction. 
 
     
     
       2. The method of  claim 1 , comprising an additional step of:
 b. if the start speed and the end speed are both below the predetermined threshold values therefor, respectively, then performing the shuttle shift by changing the direction of operation of the transmission and the direction of tilt of the swash plate while holding the vehicle at least substantially stationary. 
 
     
     
       3. The method of  claim 2 , wherein at least one of the steps of performing the shuttle shift comprises decelerating vehicle during at least a portion of the shift, and prior to or during the shuttle shift a step will be performed including determining whether a temperature of a first element will or does exceed a predetermined threshold value therefor, and:
 i. if no, then performing the shuttle shift using the first element for the deceleration; and 
 ii. if yes, then performing the shuttle shift in a different manner without using the first element for the deceleration. 
 
     
     
       4. The method of  claim 3 , wherein the step of determining whether the temperature of the first element will exceed the threshold value comprises modeling the temperature as a function of at least a history of usage of the first element. 
     
     
       5. The method of  claim 3 , wherein the first element comprises a parking brake of the vehicle, and the second element comprises at least one clutch of the transmission. 
     
     
       6. The method of  claim 3 , wherein the first element comprises at least one clutch of the transmission and the second element comprises a parking brake of the vehicle. 
     
     
       7. The method of  claim 3 , wherein the step of determining whether the temperature of the predetermined first element will exceed the threshold value comprises modeling the temperature as a function of at least one variable. 
     
     
       8. The method of  claim 1 , wherein if the start speed is greater than a predetermined value, then the speed of the vehicle will be decreased prior to performing step a. 
     
     
       9. The method of  claim 1 , wherein the step of changing the direction of operation of the transmission comprises a sequence of disengaging a first directional clutch and engaging a second directional clutch. 
     
     
       10. A method of automatically operating a continuously variable hydro-mechanical transmission of a vehicle, comprising steps of:
 monitoring an operator controlled input device for inputted commands indicative of a commanded shuttle shift; then 
 determining a start speed of the shift and an end speed of the shift, and, selecting a manner of performing the shuttle shift at least partially as a function of the speeds; wherein 
 a. if the speeds are above threshold values therefor, respectively, then initiating the shuttle shift while still moving by reversing a direction of operation of an input of the transmission while maintaining a displacement and a direction of operation of a hydrostatic power unit thereof substantially constant; or 
 b. if at least one of the start speed and the end speed are below the threshold value therefor, then changing the displacement of the hydrostatic power unit to slow the speed of the vehicle to about zero, reversing the direction of operation of the hydrostatic power unit and changing the displacement thereof to achieve the end speed. 
 
     
     
       11. The method of  claim 10 , wherein at least one of the shuttle shift steps will include decelerating the vehicle during at least a portion thereof using a predetermined first element, and wherein the method includes a step prior to step a. of determining whether a temperature of the first element will exceed a predetermined threshold value therefor, and:
 i. if no, then performing the shuttle shift using the first element for the deceration; and 
 ii. if yes, then performing the shuttle shift using a second element for the deceleration. 
 
     
     
       12. The method of  claim 11 , wherein the step of determining whether the temperature of the first element will exceed the threshold value comprises modeling the temperature as a function of at least a history of usage of the first element. 
     
     
       13. The method of  claim 11 , wherein the first element comprises a parking brake of the vehicle, and the second element comprises at least one clutch of the transmission. 
     
     
       14. The method of  claim 11 , wherein the first element comprises at least one clutch of the transmission and the second element comprises a parking brake of the vehicle. 
     
     
       15. The method of  claim 11 , wherein the step of determining whether the temperature of the predetermined first element will exceed the threshold value comprises modeling the temperature as a function of at least one variable. 
     
     
       16. The method of  claim 15 , wherein the at least one variable comprises a history of use of the first element. 
     
     
       17. The method of  claim 10 , wherein the step of changing the direction of operation of the transmission comprises a sequence of disengaging a first directional clutch and engaging a second directional clutch. 
     
     
       18. A method of automatically operating a continuously variable hydro-mechanical transmission of a vehicle, comprising steps of:
 monitoring an operator controlled input device for inputted commands indicative of a commanded shuttle shift; 
 determining a start speed of the shift and an end speed of the shift; 
 modeling a temperature of at least a first element configured and operable for holding or decelerating the vehicle during the shuttle shift; and 
 selecting a manner of performing the shuttle shift by either changing a direction of operation of the transmission while holding a displacement of a hydrostatic power unit thereof substantially constant, or by reducing the speed to about zero and holding the vehicle while changing the direction of operation and a direction of the displacement, as a function of an analysis of the start and end speeds and the modeled temperature. 
 
     
     
       19. The method of  claim 18 , wherein the first element comprises a parking brake of the vehicle, the analysis comprises determining if the modeled temperature is above a threshold, and if yes, then holding the vehicle during the shuttle shift using an element other than the parking brake. 
     
     
       20. The method of  claim 18 , comprising an additional step of modeling a temperature of a second element configured and operable for holding the vehicle during the shuttle shift; and wherein the step of selecting the manner of performing the shuttle shift additionally includes analyzing the modeled temperature of the second element. 
     
     
       21. The method of  claim 20 , wherein the second element comprises at least one range clutch of the transmission.